Kajuan Raye, 19, was shot in the back, according to the medical examiner. The officer who fired the shot claimed Raye pointed a gun at him, but investigators have yet to find a gun.

"There was no gun. There still is no gun. And there won't be a gun, because Kajuan did not have a gun. He was unarmed," attorney Michael Oppenheimer said.

Chicago Police Superintendent Eddie Johnson has already taken the strongest action he can by stripping the officer of his police powers. But on Tuesday, Raye's family filed a federal lawsuit against the city and the officer, who they identify as Sgt. John Poulos.

It is the second time in less than three years that Poulos has shot and killed a suspect. In 2013, he was off duty when he confronted Rickey Rozelle as he allegedly tried to break into a vacant apartment.

Investigators never found a gun near Rozelle. The shooting was determined to be "justified" by the Independent Police Review Authority, though Rozelle's family has also filed a lawsuit.

"It's something that I think is unprecedented. You have the same police officer in three years' time, shooting two unarmed black men in the city of Chicago. What are the odds?" said Michael Goode, Rozelle's attorney.

In the latest case, Poulos told investigators Raye was running away and had his hand on a shiny object he thought was a gun.

"They shot him in the back when he was running away. We're all scared. If a police officer approached me, I'm gonna run, too," said Ja'Mal Green, an activist.

Supt. Johnson said that for now, he's going to let IPRA investigate and determine what happened.

"I just think each case should stand on its own merits and again, I'll wait until IPRA does its thorough investigation and we'll go from there," Johnson said.

The family is also asking the state's attorney to file criminal charges against the officer.